The Jewsleft Egypt in in 1450 BC and the book of Leviticus was written between 1440-1400 BC or later. The way of life dictated by Moses for the Jews was first lived and than written down in the book of Leviticus.
Christ was born under the law given to Moses by God. According to the Law of Moses, Jesus was circumcised on the eight day after his birth. Circumcision meant that a child became a member of God's people. Since Jesus was already the Son of God made man, why did he have to be circumcised? Because God is more farsighted than we are. St. Thomas Aquinas gives us seven reasons why this had to be so.
To prove that he had a real human body. Some have held that his body was imaginary
while other have maintained that his body was divine.
2) To show God's approval of Circumcision.
3) To prove that he was a descendant of Abraham.
4) In order to take away from the Jews an excuse not to receive him.
5) To give us an example of obedience.
6) That we might allow Him to heal our sinful flesh.
7) To set us free from the Law.
Mary remained unclean for forty days thereafter. This meant that "She shall not touch anything sacred not enter the sanctuary." (Lv 12:4) Mary and Joseph went to the temple of Jerusalem where they bought either two pigeons or turtle doves. These were given to a priest who offered them in sacrifice, one as a burnt offering and the other as a purification offering. It seems to us strange to consider human birth "unclean", yet this law made sense to the Jews. A woman giving birth was not a sinful act yet the child in her womb was in the likeness of sinful Adam or as David put it, "Behold, I was born in guilt, in sin my mother conceived me." (Ps 50:7) A child inherited the effect of Adam's sin, namely, estrangement from God, came through the fallen nature of man and woman who were also implicated in the fall of Adam and Eve, hence the need for purity before approaching the all Holy God.
Since Mary and her son were sinless, should she not be exempted from the Law of Purification? St. Thomas Aquinas states: "I answer that, As the fulness of grace flowed from Christ on to His Mother, so it was becoming that the mother should be like her Son in humility: for "God giveth grace to the humble," as is written James 4:6. And therefore, just as Christ, though not subject to the Law, wished, nevertheless, to submit to circumcision and the other burdens of the Law, in order to give an example of humility and obedience; and in order to show His approval of the Law; and, again, in order to take away from the Jews an excuse for calumniating Him: for the same reasons He wished His Mother also to fulfill the prescriptions of the Law, to which, nevertheless, she was not subject. (Summa Theologica, Pt. III, Q. 37:4)
Christ came not to destroy the Law but to fulfill it, to bring it to completion, to give the Law it final meaning.
sent his Son,
born of a woman,
born under the law,
to ransom those under the law."